Ruthenium-catalyzed selective and efficient oxygenation of hydrocarbons with water as an oxygen source
Ruthenium-catalyzed selective and efficient oxygenation of hydrocarbons with water as an oxygen source
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DOI：
10.1002/anie.200801170
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Fukuzumi, Shunichi
中科院分区：
文献类型：
--
作者：
Hirai, Yuichirou;Kojima, Takahiko;Fukuzumi, Shunichi
开发高选择性和高效率地将丰富的有机资源转化为有价值的产品的方法对于可持续发展的社会至关重要。为了实现这一目标，长期以来，人们对以金属配合物为催化剂的高效材料转化方法进行了广泛的研究。[1，2]高价金属-含氧物种是金属酶（主要是血红素和非血红素铁酶）生物氧化的关键中间体，其催化代谢和分解代谢过程中烃的氧化。[3，4]这些加氧酶涉及高价金属-氧物种作为反应性物种，其通过与质子转移偶联的分子氧的还原活化而产生。[5-7]过氧化物如过氧化氢可导致所谓的“过氧化物分流”以进行催化氧化;细胞色素P450 [8]和甲烷单加氧酶发现了这种机制。[9]因此，已经开发了许多用于这些酶促氧化的模型系统，以阐明反应机制，并利用涉及形成高价金属-氧代物种的金属络合物对外部底物进行有效的催化氧化。[10-12]这些系统通常需要有机溶剂和过量的有机或无机过氧化物作为氧化剂和氧源。此外，在这种情况下，反应途径变得复杂并产生多种产物。因此，很难控制主要由不可避免地产生的自由基物质产生的产物分布。[13另一种产生高价金属-含氧物质的策略已经在光系统II（PSII）中的放氧复合物（OEC）中被认识到，用于光合作用以氧化水产生分子氧。[15]在OEC，锰（V）-氧物种已被提出形成质子耦合电子转移（PCET），和配位水的去质子化和金属中心的氧化被认为是协调发生。[16]这种策略已被应用于形成和分离高价金属-氧代物种以进行化学计量的氧化反应;[17]然而，它还没有被应用于在水中使用过渡金属络合物作为催化剂的催化氧化。受光合作用中OEC反应的启发，我们尝试利用PCET建立一种以水为溶剂和氧源的新型催化氧化体系。[18我们在此报道了一种新的钌（IV）-氧代配合物的形成及其对各种烃在水中的高效和选择性催化氧化和氧化反应的反应性，所述烃可用作氧源。我们合成了一种新的双水相钌配合物[RuII-（tpa）（H2O）2]（PF 6）2（1; tpa=三（2-吡啶甲基）胺）（图1a，B），通过在水中用AgPF 6处理[RuIICl（tpa）] 2（PF 6）2[20]。络合物1表现出可逆的两步去质子化-质子化平衡，并且两个pKa值通过UV/维斯光谱滴定法测定（参见支持信息中的图S1），范围为
The development of methods for the highly selective and efficient conversion of abundant organic resources into valuable products is crucial for a sustainable society. To achieve this goal, extensive studies on the methodology of efficient material conversion with metal complexes as catalysts have been made for a long time.[1, 2] High-valent metal–oxo species are key intermediates in biological oxidations by metalloenzymes (mainly heme and non-heme iron enzymes), which catalyze the oxygenation of hydrocarbons in metabolic and catabolic processes.[3, 4] These oxygenases involve high-valent metal–oxo species as reactive species that arise by reductive activation of molecular oxygen coupled with proton transfer.[5–7] Peroxides such as hydrogen peroxide can lead to a so-called “peroxide shunt” to perform the catalytic oxygenation; this mechanism is found for cytochrome P450 [8] and methane monooxygenase.[9] Thus, a number of model systems for these enzymatic oxidations have been developed to elucidate the reaction mechanisms and to perform effective catalytic oxygenation of external substrates with metal complexes involving the formation of high-valent metal–oxo species.[10–12] These systems usually require organic solvents and excess amount of organic or inorganic peroxides as both oxidants and oxygen sources. Moreover, in such cases, the reaction pathways become complicated and give multiple products. Consequently it is difficult to control the product distribution that arises mainly from the inevitably produced radical species.[13, 14]Another strategy to generate a high-valent metal–oxo species has been recognized in the oxygen-evolving complex (OEC) in Photosystem II (PSII) for the photosynthesis to oxidize water to produce dioxygen.[15] At the OEC, a manganese (V)–oxo species has been proposed to be formed by proton-coupled electron transfer (PCET), and the deprotonation of coordinated water and the oxidation of the metal center are thought to occur concertedly.[16] This strategy has been applied to form and isolate high-valent metal–oxo species to perform stoichiometric oxidation reactions;[17] however, it has not been applied to catalytic oxidations with transition-metal complexes as catalysts in water. Inspired by the reactions at the OEC in photosynthesis, we have tried to establish a novel catalytic oxygenation system using water as both the solvent and the oxygen source by virtue of PCET.[18, 19] We report herein the formation of a novel ruthenium (IV)–oxo complex and its reactivity toward highly efficient and selective catalytic oxygenation and oxidation reactions of various hydrocarbons in water, which can be used as an oxygen source. We synthesized a novel bis-aqua RuII complex,[RuII-(tpa)(H2O) 2](PF6) 2 (1; tpa= tris (2-pyridylmethyl) amine)(Figure1a, b), by the treatment of [RuIICl (tpa)] 2 (PF6) 2[20] with AgPF6 in water. Complex 1 exhibits a reversible twostep deprotonation–protonation equilibrium, and the two pKa values were determined by UV/Vis spectroscopic titration (see Figure S1 in the Supporting Information) in the range of